SAN FRANCISCO — Jessica Vyvyan-Robinson was diving off Borneo when she was struck without warning by shock waves.
“I could feel it in my chest — like a dull, booming sound,” she recalled in an interview. After surfacing, her group learned that fishermen had detonated explosives.
The incident, which occurred a year ago, was Ms. Vyvyan-Robinson’s first encounter with blast fishing, a highly destructive technique used in impoverished pockets of the world.
The blasts, often from dynamite, leave craters in coral reefs and kill far more fish than can be harvested, and in many places, the tourism industry serves as a powerful voice against blast fishing, which could scare divers and other visitors away. Some nations have successfully clamped down on the practice, which is generally illegal, but it continues in areas where explosives are available and people are desperate.
The effects of blast fishing can be horrifying. Ms. Vyvyan-Robinson, who wrote about her experiences for ScubaDiverLife.com, describes finding waters littered with dead or struggling fish. Only a portion of the fish that are killed is retrieved because many sink to the bottom. Their air bladders,which help fish remain buoyant, and other internal organs can rupture.
Blast fishing is not new. It was introduced to many parts of the world by European armies, said Michel Bariche, an expert on Mediterranean marine issues at the American University of Beirut in Lebanon.
“During the First World War, soldiers used grenades to catch fish for a quick and fresh meal,” he said in an email. In Lebanon, for example, blast fishing spread after French soldiers demonstrated the technique.
The nation continues to struggle to contain the practice although it is illegal, Dr. Bariche said. Culprits often seek out areas where fish congregate, and then throw a homemade bomb among them, he said.
The explosions are generally easy to spot — and thus, in theory, easy to police — but Dr. Bariche said that over the past decade or two, some fishermen had taken to dropping explosives deeper and at night, when detection is less likely.
Some Lebanese anglers use lights at night to attract small fish before detonating the charge. As the small fish sink, he explained, they attract bigger fish, which can then be caught with the hook-and-line method. One problem with this practice is that shrimp, crab and lobster larvae are also drawn to the light and killed.
Tanzania has seen a resurgence in blast fishing over the last decade as mining and construction activity in the country have made it easier to obtain dynamite.
“It looks like an old World War II movie where they throw depth charges in the water,” said Marcel Kroese, who works on the SmartFish Program, an effort financed by the European Union to improve Africa’s fisheries.
Fishermen often resort to dynamite around coral reefs, where nets might snag, Mr. Kroese said. The Tanzanian coast also has relatively few fish, so anglers are desperate to harvest anything they can.
A pilot acoustic study over six weeks last year in Tanzania for the World Wildlife Fund, an environmental group, estimated that 19 blasts per day occurred in one small stretch of water not far from Dar es Salaam, the largest city. More blast-detection microphones will be deployed soon, according to Jason Rubens, a W.W.F. Tanzania representative.
The Tanzanian government and tourism officials would like to combat the problem, Mr. Kroese said, but have lacked the resources. The destruction of small fish and coral reefs receives far less attention than another environmental problem: the poaching of elephants and other wildlife. But this spring the Tanzanian government plans to begin a $1 million initiative to reduce dynamite fishing, according to The Tanzania Daily News.
Kenya, concerned about terrorist attacks, has cracked down on the availability of explosives, and has essentially eliminated dynamite fishing, Mr. Kroese said.
Experts say that blast fishing remains common in parts of Southeast Asia, particularly Indonesia and the Philippines, while other countries in the region have made progress in stamping it out.
In Cambodia, blast fishing has “pretty much been stopped around the major islands” and now can be found only in outlying areas, said Paul Ferber, who runs an environmental group called Marine Conservation Cambodia.
He describes the aftermath of blast fishing as “fish flapping around in severe shock.” Pressure from the growing tourism industry had led to a government crackdown.
Cambodia encouraged fishing communities to manage their own waters, and those communities patrol and spread information about why the practice is harmful and why fishermen should prevent others from doing it.
The idea was: “If you let these guys do it, it’s you guys that are going to suffer,” Mr. Ferber said.